Switched mode power supplies as main part of telecom and commercial systems often dictate their size and electrical performance as well as reliability and costs. As requirements for the key characteristics power density and efficiency of power converters increase, the demands of these evaluation characteristics increase for inductive components particularly. One approach of increasing the power density and the efficiency is to integrate inductive components. Transformers and inductors can be integrated into a single magnetic structure which than reduces cost, increases power density and power efficiency.
A circuit where integrated magnetics are strongly recommended is the LLC resonant converter, which is capable of yielding high efficiency and high-quality EMI while operating at high switching frequency. Resonant converters, in particular LLC resonant converters, have a growing popularity due to their high efficiency, low level of EMI emissions, and ability to achieve high power density. Further advantages are small size, light weight and high efficiency.
Moreover, the interleaving method, i.e. combining multiple single LLC resonant converters, in particular in parallel connections, is commonly used in modern power supply designs to increase the maximum output power per unit, to spread power losses, to apply phase shedding in light load operation and to decrease the size of input and output filters. Additional measures such as active current sharing control are usually necessary for interleaved converters to balance the load among the single converters.
By interleaving two LLC converters volume of bulky components can be reduced and better current distribution can be achieved. Also, due to current ripple cancellation effect, volumes of input and output filters can be reduced substantially. Arrangement with interleaved LLC converters are for instance disclosed by U.S. Pat. No. 8,564,976 and US 2014/0009985 A1. An LLC converter uses three magnetic components: a series resonant inductor, a parallel resonant inductor, a two-winding or three-winding transformer. When two LLC converters are interleaved that number of magnetic components doubles. This converter results, additionally to the number of discrete magnetic components which yield higher size and costs, in at least six windings and several interconnections which negatively impact the efficiency.
In recent years some efforts were done to integrate all three magnetic components into a single component for LLC resonant converter. US 2008/0224809 discloses an arrangement where the parallel resonant choke is integrated in the transformer by introducing an air gap in the transformer which set the magnetizing inductance. An integrated magnetic structure, with transformer and series resonant integrated, helps to increase power density as well as efficiency. Core losses are reduced by means of flux compensation in mutual core flanges and copper losses are minimized by reduction of interconnections between resonant choke and transformer. Mutual core flanges also imply increase of power density.
Despite the component integration there are still two magnetic assemblies for the two interleaved LLC converters. Core integration can be used in order to cancel the flux in mutual core segment and therefore reduce core losses and volume resulting in higher efficiency and power density.
US 2016/0254756 A1 recently disclosed an integrated magnetic component for a three phase interleaved LLC converter, comprising three series resonant inductors, three parallel inductors and three transformers. This integrated magnetic component implements automatic current equalization and achieves an effect of automatic balancing currents in all branches. However by the strong coupling of the currents design of the components becomes more complex. A structure is needed which reduces overcall core size as well as copper losses and increases the power density without negatively impacting the EMI quality. Structures suitable for two interleaved LLC converters as depicted in FIG. 1 are subject-matter of this invention.
The present interleaved power converters are either bulky or they require numerous magnetic components, or they involve a significant effort in engineering due to strong coupling between the components of the single LLC converters.